Bubble machine



FIG. 1 is a perspective view of a bubble machine in accordance with our design;

FIG. 2 is a side elevation view thereof, the opposite view being a mirror image of that shown;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a back elevation view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines are included for the purpose of illustrating portions of the bubble machine that form no part of the claimed design. 

The ornamental design for a bubble machine, as shown and described. 